Effect of atmospheric pressure plasma treatments for enhanced adhesion of arc-sprayed zinc coatings on CFRP substrates

Surface metallization of carbon-fiber-reinforced polymer (CFRP) is increasingly required for multifunctional lightweight structures, yet achieving strong adhesion between metallic coatings and polymer-based composites remains a critical challenge due to low surface energy and surface contamination. This study addresses this challenge by systematically investigating atmospheric pressure air and argon plasma treatments (APPT) as an environmentally friendly and scalable surface-activation strategy to enhance bonding between CFRP substrates and arc-sprayed Zn coatings. Comprehensive characterizations, including SEM, AFM, 3D profilometry, contact angle/surface energy analysis, FTIR, and XPS analysis revealed that APPT did not significantly alter microscale roughness but critically transformed surface chemistry. The results showed that argon plasma ablated surface epoxy layer, led to increased surface energy with exposed carbon fibers (CFs). This facilitates direct mechanical interlocking between the exposed CFs and the incoming Zn, resulting in enhanced adhesion. Air plasma produced a dual effect by additionally generating oxygen-rich functional groups (–COOH, –OH), thereby enabling hydrogen bonding with ZnO species and markedly increasing polar surface energy (72.08 mJ/m²). Pull-off adhesion strength improved substantially for both plasma-treated CFRP, reaching a maximum of 4.21 ± 0.12 MPa for the most intense air plasma-treated CFRP, representing an 84% increase over untreated CFRP. Failure mode shifted from adhesive to predominantly cohesive, and CZM simulation confirmed enhanced interfacial adhesion and delamination resistance. Overall, APPT, especially, air plasma provides an effective and industrially viable route for activating CFRP surfaces and achieving robust CFRP/Zn bonding for advanced composite–metal systems.